Question

which number is not define??? is the not define reflect on the number line?​

Answer 1

Real numbers = All numbers on the number line

Yes and this doesn't mean that real numbers = all numbers usually written down this line, but all numbers that could be represented as a point on this line.

My understanding was ..,-3,-2,-1,0,1,2,3,.. made up the number line.

That numbers are only the points on the number line.

UPDATE:

Representations of a number line may vary.